(1) Field of the Invention
This invention relates to a fuel injection control device for an internal combustion engine, and more particularly to such a fuel injection control device which enables injection of fuel into separate cylinders to be controlled by one timer, without reference to the number of cylinders, thereby simplifying the configuration of an electronic circuit for the control of the internal combustion engine, reducing cost, and improving reliability.
(2) Description of the Prior Art
FIG. 1 is a block diagram schematically illustrating the structure of a conventional fuel injection control device for an internal combustion engine, FIG. 2 is a time chart for describing the operation of the fuel injection control device shown in FIG. 1, and FIG. 3 is a flow chart for describing the operation of a computer (hereinafter referred to as "CPU") part of the device of FIG. 1. In the diagram of FIG. 1, the input and output interfaces are omitted.
A top dead center (TDC) signal for any of the cylinders is issued when the piston of that particular cylinder is substantially at the top dead center thereof. It serves to indicate the standard timing for starting the fuel injection for the cylinder.
A fuel injection discriminating signal IIS is issued whenever one cycle of fuel injection for all cylinders is completed. This signal is given out after every second rotation of the crank.
The top dead center signal TDC is given a definite shape in a waveform shaper 10 and then supplied to a cycle counter 14 and a CPU 20. The injection discriminating signal IIS is given a definite shape in a waveform shaper 11 and then supplied to the set terminal of a flip-flop 12.
The flip-flop 12 functions as an injection discriminating flag. The Q output from the flip-flop 12 is supplied to the CPU 20.
A PB sensor signal PBS, a throttle signal THS, a water temperature signal WTS, and an air temperature signal ATS are invariably supplied to a multiplexer 16, converted into digital signals in an A/D converter 18 in accordance with selection commands from the CPU, and then taken into the aforementioned CPU 20.
A read only memory (ROM) 21 is used to store programs for the CPU 20, and a random access memory (RAM) 22 stores data for arithmetic operations and results of the arithmetic operations. Plainly, the output of the cycle counter 14, i.e. the interval between the successive top dead center signals TDC or the cycle of the top dead center signal TDC, corresponds to the revolution number of the engine. By the well-known method using the output of the cycle counter 14, the PB sensor signal PBS, or the throttle signal THS, therefore, a basic fuel injection time signal Ti can be read out of a table, for example.
The basic fuel injection time signal Ti is corrected into an actual fuel injection time signal Ta by the well-known technique using the water temperature signal WTS and the air temperature signal ATS, for example.
The CPU 20 selects the particular one of the injectors to be controlled as described fully afterward in accordance with the timings of occurrence of the top dead center signal TDC and the injection discriminating signal IIS and supplies the output (actual fuel injection time signal Ta) to the corresponding one of #1 through #4 timer counters, 31 through 34.
The timer counter to which the output corresponding to the actual fuel injection time signal has been supplied by the CPU 20 feeds a drive signal to the corresponding one of the #1 through #4 drivers, 41 through 44 and, at the same time, starts clocking the time.
The aforementioned driver is stopped after the time fixed by the aforementioned actual fuel injection time signal Ta has elapsed.
In the manner described above, the control over each of the injectors, namely the control of the fuel fed to the corresponding cylinder, is carried out.
Now, the operation of the CPU 20 will be described with reference to FIG. 3.
Step S1--This step discriminates between the presence and the absence of the input of the top dead center signal TDC. PA0 Step S2--This step adds 1 to the value in the TDC counter when the presence of the input of the top dead center signal TDC is found in step S1. PA0 Step S3--This step reads in the output of the cycle counter 14 and the PB sensor signal PBS or the throttle signal THS. PA0 Step S4--This step, based on the data read in through the preceding step, reads out the basic fuel injection time signal Ti from a two dimensional table by using the output of the cycle counter 14 and the PB sensor signal PBS, for example, as parameters. PA0 Step S5--This step discriminates the state of acceleration or deceleration based on the ratio of change of the throttle signal THS, i.e. .DELTA.th/.DELTA.t, and corrects the aforementioned basic fuel injection time signal Ti by a proper known technique using the outcome of the discrimination. PA0 Step S6--This step reads in the water temperature signal WTS and the air temperature signal ATS, for example, through the multiplexer 16 and the A/D converter 18 and corrects the aforementioned signal Ti by a proper known technique in accordance with the values of such signals. The outcome of this step is the actual fuel injection time signal Ta. PA0 Step S7--This step determines whether the flip-flop (injection discriminating flag ) 12 is set or not. When the flip-flop is set, the operation proceeds to step S8. However, when the flip-flop is not set, the operation proceeds to step S9. PA0 Step S8--This step resets the flip-flop (injection discriminating flag ) 12 and, based on the actual injection time signal Ta found previously by calculation, energizes the #1 timer counter 31 and causes the fuel to be supplied in a stated amount to the first cylinder by the operation of the #1 driver 41 and the #1 injector 51. PA0 Step S9--This step determines whether the value of count in the TDC counter is 2 or not. PA0 Step S10--This step energizes the #2 timer counter 32 and causes injection of the fuel in a stated amount through the #2 injector 52, based on the actual injection time signal Ta found by calculation in preceding step S6. PA0 Step S11--This step determines whether the value of count in the TDC counter is 3 or not. PA0 Step S12--This step energizes the #3 timer counter 33 and causes injection of the fuel in a stated amount through the #3 injector 53, based on the actual injection time signal Ta found by calculation in preceding step S6. PA0 Step S13--This step energizes the timer counter #4, 34 and causes the fuel to be supplied in a stated amount through the #4 injector 54, based on the actual injection time signal Ta found by calculation in preceding step S6. PA0 Step S14--This step resets the TDC counter and returns the operation to step S1.
In FIG. 1, the #1 timer counter 31 is depicted as formed in one block. Actually, however, it is composed of a register for memorizing the actual fuel injection time signal Ta mentioned above, a timer for clocking time in accordance with the start signal from the CPU 20, and a comparator for comparing the memorized signal of the aforementioned register and the counted value of the aforementioned timer. The #1 driver 41 is energized by the start of the aforementioned timer to open the #1 injector 51. When the comparator produces its output, the #1 driver is deenergized so as to close the valve of the #1 injector 51.
The operation described above exactly applies to each of the other timers 32-34.
In accordance with the fuel injection control device for the internal combustion engine illustrated in FIG. 1, the optimum injection time or the optimum amount of fuel to be injected is calculated for each of the cylinders of the internal combustion engine at every optimum time to efect sequential fuel injection at the optimum timing as described above.
The sequential fuel injection effected in this manner, as viewed in terms of the demand made by the engine, proves to be the most desirable method for the control of fuel injection.
This method requires all the cylinders of the internal combustion engine to be severally served by timer counter circuits, e.g. at least four timer counter circuits in the case of a four-cylinder engine, so that fuel injection signals will be issued one each for all the cylinders. It, therefore, entails a disadvantage that the electric control circuit is so complicated in configuration as to induce addition to cost and reduction in reliability of performance.
Further when the internal combustion engine is operated under the condition of a heavy load, the aforementioned merit of and the necessity for the sequential control are diminished because the fuel injection times are proportionally elongated.